Question

Two convex lens each of focal length 20 cm are separated by 125 cm. An object of height 0.5 cm placed at distance 25 cm left side from the first lens then, find height of the final image. (1) 4 cm (2) 2 cm. (3) 0.5 cm (4) 8 cm.​

Answer 1

Answer:

thats all hope it helps

Answer 2

The height of the final image is 8 cm.

(4) is correct option.

Explanation:

Given that,

Focal length = 20 cm

Height = 0.5 cm

Object distance = 25 cm

We need to calculate the image distance

Using formula of lens

$\dfrac{1}{f}=\dfrac{1}{v}-\dfrac{1}{u}$

Put the value into the formula

$\dfrac{1}{20}=\dfrac{1}{v}-\dfrac{1}{-25}$

$\dfrac{1}{v}=\dfrac{1}{20}-\dfrac{1}{25}$

$v=100\ cm$

We need to calculate the object distance of second lens

$u'=d-v$

$u'=-(125-100)$

$u'=25$

We need to calculate the image distance

Using formula of lens

$\dfrac{1}{f'}=\dfrac{1}{v'}-\dfrac{1}{u'}$

Put the value into the formula

$\dfrac{1}{20}=\dfrac{1}{v'}-\dfrac{1}{-25}$

$\dfrac{1}{v'}=\dfrac{1}{20}-\dfrac{1}{25}$

$v'=100\ cm$

We need to calculate the magnification

Using formula of magnification

$M=\dfrac{v}{u}\times\dfrac{v'}{u'}=\dfrac{h'}{h}$

$M=\dfrac{100}{-25}\times\dfrac{100}{-25}$

$\dfrac{h'}{h}=16$

$h'=16 h$

$h'=16\times0.5$

$h'=8\ cm$

Hence, The height of the final image is 8 cm.

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